1. Field of the Invention
The present invention relates to a switch container for hermetically encapsulating switch members, particularly to a switch container comprising a hollow ceramic body for hermetically encapsulating switch members, and a method for producing the switch container.
2. Description of the Related Art
Conventionally, a switch such as a vacuum switch and a circuit contactor used for shutting-off or switching electrical power, has generally employed a cylindrical ceramic tube comprising at least 85% by weight of alumina, in view of the strength, insulation and air-tightness required for the switch container.
In a conventional process of forming the cylindrical ceramic tube, a slurry of alumina is spray-dried into a powder, and then the powder is placed into a rubber mold and pressed into a green (unfired) cylindrical ceramic body. A firing temperature exceeding 1500° C. is normally needed to fire or rather sinter the green cylindrical ceramic body, due to the high alumina content thereof.
In order to encapsulate, and more particularly, hermetically seal various switch members inside the switch container, both open ends of the ceramic cylindrical tube are circularly metallized. Furthermore, two metallic end caps are each brazed onto the metallized ends so as to hermetically seal the switch members therein, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2003-2768.
3. Problems to be Solved by the Invention
When a high alumina content of at least 85% by weight is employed for producing a ceramic cylindrical body, it is difficult to carry out extrusion-molding due to the high alumina content. This is one of the main reasons why the powder-pressing process, which requires the spray-drying of an alumina slurry and additional complicated works, has been conventionally adopted for forming the cylindrical ceramic body.
Since a very high temperature of more than 1500° C. has been required to obtain an airtight ceramic container having a high alumina content for use in a vacuum switch, etc., the processing cost, including furnace cost and energy cost for producing a high-alumina content ceramic body, has been a substantive problem.
Notably, air-tightness is one of the most important requirements for a vacuum switch and a circuit contactor. A circuit contactor for use in a hybrid or electric engine using a high power battery or capacitor requires hermetic encapsulation of a non-oxidative gas such as hydrogen inside the contactor.